Affiliation: Department of Microbiology and Immunology, The University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Drive, MC-7758, San Antonio, TX 78229, USA.

ABSTRACT

Background: Oncolytic virotherapy for cancer treatment utilizes viruses for selective infection and death of cancer cells without any adverse effect on normal cells. We previously reported that the human respiratory syncytial virus (RSV) is a novel oncolytic virus against androgen-independent PC-3 human prostate cancer cells. The present study extends the result to androgen-dependent prostate cancer, and explores the underlying mechanism that triggers RSV-induced oncolysis of prostate cancer cells.

Results: We show that RSV imposes a potent oncolytic effect on LNCaP prostate cancer cells. RSV infectivity was markedly higher in LNCaP cells compared to the non-tumorigenic RWPE-1 human prostate cells. The enhanced viral burden led to LNCaP cell apoptosis and growth inhibition of LNCaP xenograft tumors in nude mice. A functional host immune response did not interfere with RSV-induced oncolysis, since growth of xenograft tumors in syngeneic C57BL/6J mice from murine RM1 cells was inhibited upon RSV administration. LNCaP cells failed to activate the type-I interferon (IFNα/β)-induced transcription factor STAT-1, which is required for antiviral gene expression, although these cells could produce IFN in response to RSV infection. The essential role of IFN in restricting infection was further borne out by our finding that neutralizing IFN activity resulted in enhanced RSV infection in non-tumorigenic RWPE-1 prostate cells.

Conclusions: We demonstrated that RSV is potentially a useful therapeutic tool in the treatment of androgen-sensitive and androgen-independent prostate cancer. Moreover, impaired IFN-mediated antiviral response is the likely cause of higher viral burden and resulting oncolysis of androgen-sensitive prostate cancer cells.

Mentions:
Deregulation of IFN-mediated antiviral response could occur due to either insufficient IFN production from cancer cells, or a dysfunctional IFN-activated JAK/STAT antiviral pathway. RSV-infected LNCaP cells produced high levels of IFN - even more than RWPE-1 cells (Figure 8a). However, the antiviral activity of IFN (as measured from the viral titer of the RSV-infected cells) was at least 100-fold higher in the case of RWPE-1 and PC-3 compared to LNCaP cells (Figure 8b). For these experiments (Figure 8b), cells were pre-treated with IFN for 16 h, followed by RSV infection in the continued presence of IFN. The viral titer was measured by performing plaque assay of medium supernatants. Representative plaque assay shows that IFN treatment caused drastic reduction of RSV infectivity in RWPE-1 (12 h and 24 h post-infection), while failing to significantly inhibit RSV infectivity/replication in LNCaP cells at 12 h and 24 h post-infection (Figure 8c). In contrast to LNCaP cells, PC-3 cells were protected against RSV to the antiviral action of IFN, since IFN treatment of PC-3 cells drastically inhibited virus replication (Figure 8d). In the absence of protection from IFN, RSV has selective growth advantage in LNCaP cells over RWPE-1 cells and PC-3 cells. Indeed, the IFN neutralizing antibody, which inhibited IFN-α/β mediated antiviral activity in RWPE-1 cells, caused significant elevation of the RSV titer in RWPE-1 cells (by approximately 15 fold), representing enhancement of viral infectivity by 750% (Figure 9a). A representative result from plaque assay of RSV-infected RWPE-1 cells that were pretreated with either control antibody or IFN-neutralizing antibody shows elevated viral titer in cells devoid of IFN response (Figure 9b). Results from Figure 9 demonstrate that IFN plays an important role in limiting RSV infection in RWPE-1 and PC-3 cells, whereas lack of this restriction in LNCaP cells associated with excessive viral replication and oncolysis.

Mentions:
Deregulation of IFN-mediated antiviral response could occur due to either insufficient IFN production from cancer cells, or a dysfunctional IFN-activated JAK/STAT antiviral pathway. RSV-infected LNCaP cells produced high levels of IFN - even more than RWPE-1 cells (Figure 8a). However, the antiviral activity of IFN (as measured from the viral titer of the RSV-infected cells) was at least 100-fold higher in the case of RWPE-1 and PC-3 compared to LNCaP cells (Figure 8b). For these experiments (Figure 8b), cells were pre-treated with IFN for 16 h, followed by RSV infection in the continued presence of IFN. The viral titer was measured by performing plaque assay of medium supernatants. Representative plaque assay shows that IFN treatment caused drastic reduction of RSV infectivity in RWPE-1 (12 h and 24 h post-infection), while failing to significantly inhibit RSV infectivity/replication in LNCaP cells at 12 h and 24 h post-infection (Figure 8c). In contrast to LNCaP cells, PC-3 cells were protected against RSV to the antiviral action of IFN, since IFN treatment of PC-3 cells drastically inhibited virus replication (Figure 8d). In the absence of protection from IFN, RSV has selective growth advantage in LNCaP cells over RWPE-1 cells and PC-3 cells. Indeed, the IFN neutralizing antibody, which inhibited IFN-α/β mediated antiviral activity in RWPE-1 cells, caused significant elevation of the RSV titer in RWPE-1 cells (by approximately 15 fold), representing enhancement of viral infectivity by 750% (Figure 9a). A representative result from plaque assay of RSV-infected RWPE-1 cells that were pretreated with either control antibody or IFN-neutralizing antibody shows elevated viral titer in cells devoid of IFN response (Figure 9b). Results from Figure 9 demonstrate that IFN plays an important role in limiting RSV infection in RWPE-1 and PC-3 cells, whereas lack of this restriction in LNCaP cells associated with excessive viral replication and oncolysis.

Bottom Line:
LNCaP cells failed to activate the type-I interferon (IFNα/β)-induced transcription factor STAT-1, which is required for antiviral gene expression, although these cells could produce IFN in response to RSV infection.We demonstrated that RSV is potentially a useful therapeutic tool in the treatment of androgen-sensitive and androgen-independent prostate cancer.Moreover, impaired IFN-mediated antiviral response is the likely cause of higher viral burden and resulting oncolysis of androgen-sensitive prostate cancer cells.

Affiliation:
Department of Microbiology and Immunology, The University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Drive, MC-7758, San Antonio, TX 78229, USA.

ABSTRACT

Background: Oncolytic virotherapy for cancer treatment utilizes viruses for selective infection and death of cancer cells without any adverse effect on normal cells. We previously reported that the human respiratory syncytial virus (RSV) is a novel oncolytic virus against androgen-independent PC-3 human prostate cancer cells. The present study extends the result to androgen-dependent prostate cancer, and explores the underlying mechanism that triggers RSV-induced oncolysis of prostate cancer cells.

Results: We show that RSV imposes a potent oncolytic effect on LNCaP prostate cancer cells. RSV infectivity was markedly higher in LNCaP cells compared to the non-tumorigenic RWPE-1 human prostate cells. The enhanced viral burden led to LNCaP cell apoptosis and growth inhibition of LNCaP xenograft tumors in nude mice. A functional host immune response did not interfere with RSV-induced oncolysis, since growth of xenograft tumors in syngeneic C57BL/6J mice from murine RM1 cells was inhibited upon RSV administration. LNCaP cells failed to activate the type-I interferon (IFNα/β)-induced transcription factor STAT-1, which is required for antiviral gene expression, although these cells could produce IFN in response to RSV infection. The essential role of IFN in restricting infection was further borne out by our finding that neutralizing IFN activity resulted in enhanced RSV infection in non-tumorigenic RWPE-1 prostate cells.

Conclusions: We demonstrated that RSV is potentially a useful therapeutic tool in the treatment of androgen-sensitive and androgen-independent prostate cancer. Moreover, impaired IFN-mediated antiviral response is the likely cause of higher viral burden and resulting oncolysis of androgen-sensitive prostate cancer cells.